The present invention relates to a light-sensitive composition which comprises a photo-crosslinkable polymer which can crosslink through a photo-dimerization reaction and a novel sensitizer, and in particular to a light-sensitive composition useful as a light-sensitive layer of a presensitized plate for use in making a lithographic printing plate (hereunder referred to as "PS plate"), as well as a photoresist or the like.
Photo-crosslinkable materials which can crosslink through a photo-dimerization reaction have been well-known and they are used as a principal component of light-sensitive compositions used for preparing PS plates, photoresists or the like. These photo-crosslinkable polymers do not show sufficient light-sensitivity. Therefore, when a PS plate or the like is prepared from such a photo-crosslinkable material, a sensitizer is in general used for enhancing the sensitivity of the resulting light-sensitive composition. Examples of such sensitizers are thioxanthone, benzophenone, Michler's ketone, anthraquinone, anthracene, chrysene, p-dinitrobenzene, 2-nitrofluorenone and merocyanine type dyes. The sensitivity of the composition is improved to some extent by the use of such a sensitizer, but is still insufficient. In addition, naphthothiazoline type dyes as disclosed in U.S. Pat. No. 2,732,301 and 2-(heterocyclylcarbo nylmethylene)thiazoline-containing merocyanine dyes as disclosed in U.S. Pat. No. 4,062,686 are useful as sensitizers for light-sensitive printing materials, but the sensitivity achieved by these compounds is still insufficient. Thus, there have been a demand for the development of more highly sensitive sensitizers.